Rap music is not polite. It's a noisy 'n' crude attack on mainstream sensibilities that has even liberal-minded adults who were raised on the rebellious, outlaw beat of Little Richard and the Rolling Stones asking themselves, "What happened to real music?"

While these adults shudder at the sound of rap, however, the music is the pulse of a far wider urban hip-hop phenomenon--a glorious, multilayered celebration of spontaneous, street-ignited artistry that also includes break dancing, graffiti and video. Its energy and flash and style have moved into advertising, fashion, and--of course--the pop-music mainstream.

Sales of rap records to young fans--black and white--have become strong enough to even make the once-reluctant pop Establishment finally open its doors to the black street sound. The Grammy Awards introduced a rap category this year, and Billboard magazine followed suit with its own rap sales chart. MTV dishes up a weekly rap show, and critics toast the best rap with a fervor rarely seen since the arrival of new-wave rock in the late '70s.

One reason for the greater acceptance is the arrival of a new wave of rappers, such as D.J. Jazzy Jeff & the Fresh Prince. They're so wholesome they could be regulars on the Cosby show.

But even with this new-found acceptance and poplarity, rap is still criticized by some who say that much of the music is socially irresponsible.

Nowhere is this outlaw rap more visible than in Los Angeles, where Compton's N.W.A has become an explosive new force with tales of gang violence that make even some in the rap movement uneasy.

Pushing the imagery much further than anyone before them, N.W.A feature sirens and gunshots as backdrops to their brutal and ugly X-rated tales of drug dealing, gangbanging and police confrontations. The group's first album, "Straight Outta Compton" has sold nearly 500,000 copies in just six weeks, while the solo album by N.W.A leader Eazy-E, "Eazy-Duz-It," is nearing the 650,000 mark.

Ice-T, a pioneer of the Los Angeles movement who calls his management-production company Rhyme Pays, goes out of his way in interviews to warn against the gang life style. His records, he has said, show young rap fans the consequences of such actions. Ice-T wrote the title track for the controversial gang movie of last year, "Colors."

The defiant N.W.A, however, refuses to pass judgment or offer itself as a role model. The group's name echoes its bold, incendiary nature: Niggers With Attitude.

Sample line from N.W.A's "Gangsta Gangsta":

Since I was a youth, I smoke weed out

Now, I'm the ----------- that you read about.

Taking a life or two.

That's what the hell I do

If you don't like how I'm living,

Well, ---- you.

This is a gang and I'm in it.

Ice Cube, a 19-year-old who writes most of N.W.A's rhymes, says the extreme language isn't just an attempt to shock. It is a reflection of N.W.A's world.

"We make these records for our people first," he said last week. "Words like bitch and nigger may be shocking for somebody who is white, but that's not why we use them. It's everyday language of people around my neighborhood. When they refer to a girl, they might say 'bitch' or when referring to a guy, they might say, 'that nigger over there.' It's not used by us the way (bigots) used to use it."

About the group's social stance, Ice Cube (real name O'Shay Jackson) added, "People say our music inspires violence or whatever, but there has been violence since the beginning of time. I like my records to shake people up, make them think . . . see something in a new way.

"To me, films like 'Cry Freedom' and ' Mississippi Burning' are from the wrong point of view. Hollywood never shows it from the black person's point of view, . . . Even in 'Colors,' they showed it from the police point of view instead of the gangbangers' point of view. Our stuff is more or less documentary. It's what we grew up with.

"People think that kids are incapable of knowing what is right and what is wrong, but kids are smarter than the adults think they are. They don't have to listen to records to know what they should do."

Because of lyrics as explosive as N.W.A's, rap has split the pop community in ways that haven't been seen since punk arrived more than a decade ago.

For nearly a decade now, much of the media and the pop Establishment has been hoping that rap would simply fade away. But the music has proved resilient and has become a dynamic forum for the expression of black frustrations and aspirations.

Dr. John Oliver, professor of social policy and planning at Cal State Long Beach's School of Social Work, sees a connection between rap and the soul artists who sang of black pride themes in the '60s.

"The rappers have gone back to the way Sly and the Family Stone or Curtis Mayfield or Donny Hathaway spoke about social conditions in the late '60s and early '70s," he said. "They are not only rallying the young rap audience into doing something actively about social problems, but also expressing black (attitudes) to the larger community.

"One of the things that made it (attractive) to young people in the beginning was that it was a way of relieving some of the anxiety and stresses they felt about being rejected by society.

"A lot of the press early on was fairly negative, but the groups were pretty tenacious, and the criticism made them more committed to it. Instead of pushing people away, I think it pushed a generation of young people closer together by giving them something of their own."

Though the commercial door was opened in 1986, when Run-D.M.C. and the Beastie Boys merged rock 'n' rap sensibilities and sold an estimated 7 million albums, the real breakthrough has occurred in the last six months.

At 2 million-plus, Tone Loc's playful "Wild Thing" is the biggest-selling single since "We Are the World" in 1985. The L.A. rapper's album is in the national Top 10 this week--one of more than two dozen rap albums to make the Billboard pop charts in recent months.

On the critical front, nine rap singles made the year's 25 best records list in a Village Voice survey of the nation's pop critics. Equally significantly, Public Enemy's political "It Takes a Nation of Millions to Hold Us Back" was voted the album of the year by a huge margin.

This turnaround is especially dramatic because rap was first dismissed by white rock fans as the enemy--some strange bastard offspring of disco. Rock radio stations resisted it. Even critics outside New York sidestepped it, except for an occasional socially conscious record such as Grandmaster Flash's "The Message" in 1982 or Run-D.M.C.'s "It's Like That" in 1983.

Some observers still look at it with disdain.

Mike Ross, who produced and arranged Tone Loc's "Wild Thing" with his partner Matt Dyke, considered rap's turnaround and said: "Every time a new phase of music comes along, people think it's just a quick trend because they don't identify with it. In this case, a lot of white people just saw rap as a bunch of black guys screaming. The music wasn't melodic or anything, and it was hard for a lot of people to relate to the songs.

"But rap isn't going to just go away. It's not just this year's disco. Disco got overexposed, and then the backlash came and boom, it was over. . . . Rap is evolving very quickly. The challenge is for the rap artists to keep changing, and there are signs now that they are capable of that change."

As Ross suggests, outsiders may say that rap all sounds the same, but there are distinct subdivisions--from the shocking street realism of Compton's Eazy-E and N.W.A to the socially minded activism of Public Enemy and Boogie Down Productions; from the girl rap vitality of Wee Papa Girls to the teen novelty of D.J. Jazzy Jeff; from the sexy strut of L.L. Cool J to the witty pop-culture salutes of De La Soul.

Reflecting on the fast-changing scene, Ross added good-naturedly: "Rap records are kind of like Kleenex for the kids. They love the record or a sound for six months and then they reach back into the box."

"Rhythmic talking over a funk beat."

That's how David Toop describes rap music in "The Rap Attack" (South End Press), his colorful and comprehensive book on the origins of this '80s offspring of such equally durable musical forms as the blues and doo-wop.

Pointing to 1979 as the start of rap as it is now known, Toop writes that the first rap records were "the tip of an iceberg--under the surface was a movement called hip-hop, a Bronx subculture, and beneath that was a vast expanse of sources reaching back to West Africa."

For Toop and other rap historians, the roots of the music stretch back through a long and surprisingly varied set of characters and movements. Toop's list includes more than two dozen cornerstones, from the lively boasts of Bo Diddley and Muhammad Ali to street groups and prison songs.

Unlike rock fans, who argue endlessly over the identity of the first true rock hit, rap fans generally point to a single record as the key beginning: the Sugarhill Gang's "Rapper's Delight."

The novelty, released by New Jersey's Sugarhill Records in 1979, only made it to No. 36 on the national charts, but it opened a door for other rappers in the Bronx.

Among those who stepped forward was Joseph Saddler, whose turntable skills helped bring a new sophistication to rap. As a kid, Saddler--who latter dubbed himself Grandmaster Flash--loved music, but records frustrated him. Rather than listen to them all the way through like everyone else, Saddler picked out the best parts and imagined how they would sound together.

By his mid-teens, he had begun to create his own records by plugging two turntables into the same speaker and playing them for neighborhood kids in the park. This twin-turntable effect enabled him to switch from one record to the other: a 10-second bass line from a James Brown record, a 15-second drum explosion from a Chic single, and so forth.

Fascinated by what Saddler was doing, other teens got into the act--either dancing to the music or rapping to it.

Seeing the success of "Rapper's Delight," Flash and his allies in the Furious Five went to Sugarhill Records and released a landmark record in rap.

Hailed as 1982's single of the year by both The Times and the New York Times, "The Message" was a stark tale of ghetto alienation that demonstrated that rap was not simply an echo of the fluffy disco era. Sample lyrics: "It's like a jungle sometimes / It make me wonder / How I keep from going under."

Grandmaster Flash and the other early rap heroes failed to step forward with consistent product or dynamic stage shows, however, and rap remained a rather limited black music experience until 1983, when two brothers from Queens entered the scene.

There are debates over who has been more important in furthering rap: Russell Simmons,who brought marketing and management skills to the virgin field, or his brother Joseph, who put together the first superstar rap act, Run-D.M.C.

Unlike many of the rap pioneers, they weren't from the Bronx or the ghetto. Raised in suburban Queens, they were sons of a supervisor of attendance for the New York City school system.

Russell got into rap by producing live rap shows and eventually managing some of the better acts, including Kurtis Blow. Today, he runs Def Jam Records--whose acts have included Public Enemy, the Beastie Boys and L.L. Cool J--and Rush Management, which represents dozens of rap acts, including Run-D.M.C., Public Enemy, Slick Rick and De La Soul.

"There was a lot of resistance to rap in the record business in the beginning, but independent labels pushed for it because it was something they could build on," Russell said in 1986. "That's how most independents get started. . . . With things that major labels don't own or care about."

Joseph Simmons was such a natural rapper that he was opening shows promoted by his brother while still in his early teens. He eventually put on his own shows at the park near his house. While studying mortuary science in college, he wrote the song that became another early rap classic, "It's Like That." The record, which is in the social-realism tradition of "The Message," sold 500,000 and pushed Run-D.M.C. into the forefront of rap.

Not only did the trio make more consistent albums than their rap rivals, but Run-D.M.C. had a greater pop-rock sensibility than its contemporaries. Without sacrificing rap's black base, Run-D.M.C. reached out to a white audience that had previously ignored rap. The group also adopted a catchy, vaguely gangster-like image incorporating black hats and clothing. The idea wasn't to make people think they were gangsters. They just thought it looked cool.

Despite the trio's wholesome messages (down with drugs, up with education), the gangster image was picked up by the media when violence broke out at a few of the group's shows and has remained a cloud over the rap industry.

When 41 fans were injured during an outbreak of gang violence at a Run-D.M.C. concert in 1986 at the Long Beach Arena, Joseph Simmons said gang violence had nothing to do with rap--that it was a symptom of larger problems in the city. For many Los Angeles residents, that violence indeed was one of the first dramatic signs of the extent of the gang problem.

Meanwhile, Run-D.M.C.--with assistance from record producer and then Def Jam co-owner Rick Rubin--added a harder edge to its music. A remake of Aerosmith's "Walk This Way" broke through to the white rock market in a big way. The single--named record of the year by the Times and the Village Voice critics' poll--reached No. 4 on the pop charts and helped push the trio's "Raising Hell" album past the 4 million sales mark.

The Beastie Boys, also working with Rubin, made an even stronger move into the rock audience with their album "Licensed to Ill." The collection, which also has sold more than 3 million, combined all the styles that parents love to hate-- punk, rap and heavy metal--in a rowdy and irreverent set of songs. They had one other quality that helped win white fans for rap: The Beasties are white.

Influenced by the success of Run-D.M.C., dozens of other rap artists surfaced. Many headed for Simmons' Def Jam Records, while others--such as the five members of N.W.A--started their own production companies.

Like early rock, rap is inexpensive to record, so acts didn't need the financial clout of a major record company to underwrite recording sessions. "Wild Thing" was made for under $500.

Jerry Heller, a record-industry veteran who over the years has been involved with such acts as Elton John and the Electric Light Orchestra, now manages N.W.A and Eazy-E, as well as more conventional black acts like Rose Royce.

"The remarkable thing about this scene is that you can make a record for a few hundred dollars," Heller said recently at the Celebrity Theatre in Anaheim, where his two bands were part of a rap bill that sold out two shows at the 2,500-seat hall.

"What that means is that you can just throw it away and try something else if it doesn't turn out right. It encourages you to try new sounds and experiment. It's not like it is at the major labels where you end up spending so much making the record, you have to put it out even if it doesn't sound any good."

In the explosion of the late '80s, rap sections of record stores have become showcases of records by strange-sounding new groups and labels. Among the latter: Delicious Vinyl, Ruthless, Select and Cold Chillin'.

Increasingly, however, major labels have begun to show up on the rap charts.

Simmons' Def Jam--distributed by Columbia Records--continues to be the most significant label. Its acts range from De La Soul, whose debut album features so many delightful pop-culture escapades that it may well be the "Sgt. Pepper" of rap, to Public Enemy, whose leader Chuck D has been hailed as the Bob Marley of rap.

Though its language can be as forceful at times as N.W.A's, Public Enemy's music has a political rather than gangbanger emphasis. The idea isn't so much to reflect life on the streets but to raise social awareness and build a renewed sense of black determination and pride.

Public Enemy's politically charged "Yo! Bum Rush the Show" album in 1987 arrived like an electric jolt. Its aggressive tales of black activism were accompanied by a stage act in which the group's aides paraded around with imitation Uzis.

When one song urged listeners to pay attention to controversial Black Muslim minister Louis Farrakhan and another seemed to condone attacks on police, there were concerns about possible anti-Semitism and irresponsibility.

Like Run-D.M.C., Public Enemy leader Chuck D (real name Carlton Ridenhour) comes from a middle-class background in the New York suburbs. During his teens, his parents sent him to a study program where some of the teachers were former Black Panther Party members. The program stressed an intense examination of black culture.

While advocating greater black unity, Chuck D made it clear in interviews after the release of the album that he wasn't urging racial separation or advocating violence.

If "Yo!" seemed chiefly directed at the black rap audience, Public Enemy's follow-up, "It Takes a Nation of Millions to Hold Us Back," was addressed equally at the new audience of whites that had become interested in rap.

About "It Takes a Nation of Millions," Chuck D said, "I wanted to put together a classic album so that years from now it would be looked at the way Marvin Gaye's 'What's Going On' or 'Sgt. Pepper's Lonely Hearts Club Band' are viewed today.

"I think we are going to see more of that ambition because rappers are discovering what it takes to make a really good album. Before, all their attention was just into getting a record out there. There were so many things working against you. . . . The radio, the record companies."

Asked if he thinks of himself more as a record maker or as a social commentator, Chuck D sighed, then said:

"It's important that we educate our people as well as entertain them. We have to walk that line, not just to our people, but people in general, . . . tell others how the black person feels about his situation in America or in the Western world.

"That's one reason there is so much confusion over rap. White audiences think they are familiar with the black experience, but they aren't. That's why they find the language and symbols sometimes shocking. And sometimes they are shocking because we are trying to get people's attention.

"When I said Uzis on the first album, I was talking about the power of words, but if I had said words , nobody would have thought twice about it. That gave us a chance to show them what we were talking about."

One of the challenges, he said, is writing songs that speak equally to black and white audiences.

"To me, that's one of the most exciting things about what's happening in rap.